The present invention relates to the field of wavelength control systems for electromagnetic radiation.
Wavelength or frequency stabilization of lasers is increasingly important for dense wavelength division multiplexed (DWDM) fiber optic systems as the spacing between channels is reduced to obtain additional system capacity. In this regard, these systems are analogous to microwave radio systems with multiplexed carriers in which the frequency stabilization of carriers has traditionally been an important issue. In a wavelength stabilized laser system, wavelength or frequency drift may be introduced by the aging or temperature dependence of the laser itself, or by the aging or temperature dependence of the optical reference filter, the optical detectors, or the stabilization electronics.
U.S. Pat. No. 5,832,014 to Johnson, which is assigned to Lucent Technologies Inc., is incorporated herein by reference in its entirety for its teachings on wavelength stabilization in tunable semiconductor lasers. Johnson describes a tunable semiconductor laser including a gain section and at least one tuning section. Spontaneous emission (SE) from the tuning section is detected and used in a feedback control loop to control the amount of current applied to the tuning section. The feedback control loop operates to maintain the detected SE at a constant level, such that the current applied to the tuning section is adjusted to compensate for the effects of aging and the laser output wavelength is thereby stabilized.
Johnson rejects a number of alternative approaches, stating that, xe2x80x9cConventional approaches to solving the wavelength stabilization problem in tunable semiconductor lasers generally involve monitoring the lasing wavelength using precise filters . . . . However, these filtering techniques can be expensive and difficult to implement in many practical applications. Moreover, the required filters are often unsuitable for integration with the semiconductor laser on a single chip.xe2x80x9d
A method and apparatus are desired that makes use of filters for wavelength stabilization in semiconductor lasers practical and effective.
The present invention is a method and system for conditioning signals from two optical detectors, including: multiplexing electrical signals from the two detectors into a single electrical path that is connected to the processor; and conditioning the signals in the single electrical path.
The invention is an improvement in a system for controlling a light source. The system has first and second optical detectors providing first and second electrical signals, respectively. The first and second electrical signals are multiplexed into a single electrical path that is connected to the processor. The signals are conditioned in the single electrical path to form conditioned signals that are used by a processor to control the light source.